Bond pads are used to transmit power and signals to an integrated circuit and should provide the lowest resistance connection possible. For this reason, bond pad integrity control (as measured by surface quality and thickness) is crucial to ensure optimum bond pad performance. The primary sources of bond pad degradation are corrosion and aluminum loss. Corrosion of the bond pads is primarily caused by environmental halide (e.g. fluoride, chloride) contamination and storage humidity. Aluminum loss occurs primarily during the bond pad etch that defines the bond pads, and post bond pad formation cleaning processing. Bond pad degradation manifests itself in various forms, such as non-stick on pad (NSOP) issues that occur when the top surface of the bond pad is corroded by halide or the passivation material covering the top level metallization is insufficiently etched. Bond pad degradation is also seen as delamination of the bond pad during application of a bond wire to a bond pad, otherwise known as wire pull reliability. Wire pull reliability is degraded when there is insufficient aluminum thickness after processing. In addition, the driving force from probe monitoring during sort aluminum loss can also result in aluminum loss.
Manufacturing process/environment abnormalities affecting bond pad integrity may result in NSOP issues during wire bonding, wire pull reliability failure, or even final test failures. The current copper-based interconnect control methodology involves using crude visual inspections to monitor the bond pad integrity during the manufacturing process. Additionally, there is no monitoring of the aluminum bond pad metal sheet resistance in place. Other methods of monitoring bond pad quality such as visual microscope inspections, energy dispersive spectroscopy (EDS) and wire pull reliability testing are sample size limited and are not sufficient to detect corrosion or thickness abnormalities on the bond pads for all wafers/dies.
It is in this context that embodiments of the invention arise.